fix: improved UTF8 handling in file transaction display

[ericleponner]

Description:

Changes below improve UTF8 handling in FileContentsModal.displayContent.

Fixes:

TT-004

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[swirlds-automation]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.98%. Comparing base (40dbd71) to head (72e2d04).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3370   +/-   ##
=======================================
  Coverage   99.98%   99.98%           
=======================================
  Files         213      213           
  Lines        6725     6725           
  Branches     1228     1230    +2     
=======================================
  Hits         6724     6724           
  Misses          1        1           

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[jbair06]

Satisfies the requirements. LGTM